1. Field
The present disclosure relates to optical communication equipment and, more specifically but not exclusively, to the use of hierarchical modulation in optical transport systems.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
As used herein, the term “hierarchical modulation” refers to a modulation technique in which multiple data streams are multiplexed into a single symbol stream. In its most basic form, hierarchical modulation has two modulation layers referred to as the base layer and the enhancement layer. In this particular hierarchical-modulation variant, each constellation point of the base layer is split into multiple constellation points using the operative constellation of the enhancement layer. In more-complex hierarchical-modulation schemes, more enhancement layers can be added by further splitting each of the constellation points corresponding to the last enhancement layer using the operative constellation of the next enhancement layer. In the literature, hierarchical modulation may also be referred to as “layered modulation.”